618 Notices respecting Neiv Boohs. 



thing from his pen is certain to reward careful reading. There 

 are three chapters. In Chapter I. the conceptions of space 

 symmetry and curvature are considered as they present themselves 

 in Euclidean space. Chapter II. is devoted to Euclidean Geometry 

 of Eour Dimensions, the particular aspects discussed being rotation 

 about a plane and the properties of the three-dimensional spheres 

 in this 1'our-dimensional spread. The final chapter is taken up 

 with a brief account of certain fundamental properties of spaces 

 with negative curvature. The outlook throughout is purely 

 geometrical, and the reader has for the most part to supply 

 mentally the geometrical figures which form the bases of the 

 arguments. 



Traite Theorique et Pratique cVElectricite. f Par H. Pecheux, Pro- 



fesseur de Physique et de Chimie a VEcole Nation ale d'jlrts et 



Metiers d'Aix. Avec Notes Additionnelles de J. Blondin et 



E. Neouloea. Preface de J. Violle. Paris : Ch. Delagrave. 



Pp. xx + 720. 



The subjects dealt with in this work cover an enormous range — 



including not only the theoretical treatment of magnetism and 



electricity, but also the more important practical applications of 



these sciences. As a record of the course of instruction provided 



at the Ecole Nationale d'Arts et Metiers the book is interesting, 



but the task attempted by the author is a very formidable one, and 



there are various blemishes in the hook which call for criticism. 



On the very first page we read : — ". . . en 1600, Gilbert, medecin 

 anglais, reconnut que d'autres substances : la resine, le caoutchouc, 

 la gutta-percha . . . selectrisent " This, if true, is very interesting 

 information indeed from a historical point of view ; but the author 

 does not explain how Gilbert came into possession of india-rubber 

 and gutta-percha. We were always under the impression that 

 iudia-rubber was unknown to the civilized world until the eighteenth 

 century, and that the introduction of gutta-percha did not take 

 place until the nineteenth century. 



In dealing with magnetism, the author repeatedly uses the term 

 " coercive force" in its old-fashioned and now generally discarded 

 meaning, and is evidently unaw r are of the new meaning given to this 

 term by Hopkinson. 



The various diagrams of magnetic fields given in the section on 

 dynamos are hopelessly wrong, not the slightest attempt being made 

 to indicate the refraction of the lines of induction as they pass 

 from air into iron, or vice versa. 



In deducing the formula for the E.M.E. of a Gramme ring:, the 

 author uses a method which we can only characterize as inconceivably 

 ponderous. 



The descriptions of dynamos, alternators, <fec. given by the 

 author are far from satisfactory, and include a number of types 

 now completely obsolete, and fit only for the museum. The author 

 himself, indeed, seems to be aware of this fact ; for in one instance, 

 at least, after describing a machine, of which an illustration is 

 given, he states that it is no longer used. Then why describe it, 

 and deliberately waste valuable space ? 



